Midlothian Council granted planning consent for a supermarket on the Arniston Rangers pitch. Sportscotland supported it but only if a new pitch was provided elsewhere. They are a community team however.
For what its worth I don't think PBS is open space but I do think the Council would say it was a pitch that needed to be replaced., Possibly an all weather pitch at Saughton. Scottish Planning Policy is just one of many documents that are considered when determining an application. The Local Development Plan should reflect the SPP but tailored towards Edinburgh. Housing, student accommodation, hotel, hostel, retail offer and a multitude of other uses would be acceptable at Tiny subject to addressing technical standards including the COMAH regulations.
If you want to see abuse of the COMAH regulations look at the blast zone for Grangemouth and how miraculously the zones bend around the Falkirk ground. Brockville is now a Morrisons so it can be done. Muirton Park is now an Asda.